The claim that this is the world's hardest sudoku puzzle was actually made by the author, and popularized by the media. There is nothing to suggest that this is the singular hardest puzzle in existence, however, it's still a pretty dern difficult puzzle.
To quote the author of the puzzle:
"Normal sudoku puzzle logic eliminates the possibilities for each box in two or three steps, but this one requires puzzlers to think ahead eight or nine steps at a time - making very long deductions to eliminate the possible candidates for each box." (source)
As this is the furthest depth we know of, and the only puzzle of this depth known, it currently takes top spot as the computationally hardest Sudoku.